Enhancing Return to Alpine Skiing: Integrating Perceptual-Motor-Cognitive Considerations in Testing and Progressions: A Clinical Commentary.

Alpine skiing poses significant risks for anterior cruciate ligament (ACL) injury at both recreational and professional levels, which is compounded by high rates of re-injury. Despite the existence of return to sport (RTS) and return to snow protocols, the frequency of ACL re-injury has not been mitigated, raising doubts about protocol effectiveness. Current RTS protocols primarily focus on biomechanical and neuromuscular factors in isolation, neglecting the important perceptual-motor-cognitive changes associated with ACL injuries and the high cognitive demands of skiing. The purpose of this clinical commentary is to address the perceptual-motor-cognitive demands specific to alpine skiing, evaluate RTS testing for skiers, and propose updated standards for testing and return to snow progressions that incorporate these considerations. Level of Evidence: 5.

Two-Portal Arthroscopic Knotless All-Suture Anchor Posterior Labral Repair.

Isolated posterior shoulder instability accounts for approximately 10% of shoulder instability cases. Patients may present after an acute trauma or with insidious onset and associated posterior shoulder pain. Knotless and all-suture anchor devices have become increasing popular and are often used in arthroscopic shoulder instability cases to avoid knot stacks and allow for the ability to re-tension the fixation. This technical note describes our technique for 2-portal posterior labral repair using knotless all-suture anchors with the patient in the lateral decubitus position.

Effect of making skin incision with electrocautery on positive Cutibacterium acnes culture rates in shoulder arthroplasty: a prospective randomized clinical trial.

BACKGROUND: Cutibacterium acnes remains the most commonly detected organism in shoulder arthroplasty. C acnes infection is thought to occur during shoulder arthroplasty through contamination of the surgical field with C acnes from the incised dermis. The purpose of this study was to examine whether using electrocautery for making skin incisions would decrease C acnes culture rates at the incised dermis compared to using scalpels during shoulder arthroplasty. METHODS: Patients undergoing primary shoulder arthroplasty were randomized into 2 groups, electrocautery vs. scalpel incision group. All patients received a standard preoperative antiseptic preparation including chlorhexidine gluconate showers, intravenous antibiotic administration, and topical application of hydrogen peroxide, povidone iodine, isopropyl alcohol, and DuraPrep. Cultures were obtained from the incised dermal edge immediately after skin incision and later from surgeon's gloves and forceps immediately prior to humeral component implantation. The primary outcome was positive C acnes culture rates compared between the groups. RESULTS: A total of 64 patients (32 in each group) were enrolled. There were 24 males in each group. Regarding dermis cultures, 10 patients (31%) in the scalpel group were positive with 8 of them positive for C acnes, whereas no patients in the electrocautery group were positive (P < .001). Regarding glove cultures, the electrocautery group had 8 patients positive C acnes, while the scalpel group had 8 (P = .777). Regarding forceps cultures, the electrocautery group had 4 patients positive for C acnes, and the scalpel group had 6 (P = .491). All positive cultures were exclusively from male patients. There were no wound complications or infection in the electrocautery group while the scalpel group had 1 acute postoperative infection. CONCLUSIONS: Making skin incisions using electrocautery resulted in 0 C acnes culture at the incised dermis, suggesting its potential effect against C acnes. However, despite this initial antibacterial effect, C acnes still appeared on surgeon's gloves and forceps during surgery of male patients. All positive cultures were from male patients, suggesting that the source of C acnes was specifically related to the male body. While the study hypothesis was supported by the results, the present study also raises new questions and calls for further research.

Metformin has anti-inflammatory effects and induces immunometabolic reprogramming via multiple mechanisms in hidradenitis suppurativa.

BACKGROUND: Targeting immunometabolism has shown promise in treating autoimmune and inflammatory conditions. Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease involving painful lesions in apocrine gland-bearing skin. Therapeutic options for HS are limited and often ineffective; thus, there is a pressing need for improved treatments. To date, metabolic dysregulation has not been investigated in HS. As HS is highly inflammatory, we hypothesized that energy metabolism is dysregulated in these patients. Metformin, an antidiabetic drug, which is known to impact on cellular metabolic and signalling pathways, has been shown to have anti-inflammatory effects in cancer and arthritis. While metformin is not licensed for use in HS, patients with HS taking metformin show improved clinical symptoms. OBJECTIVE: To assess the effect and mechanism of action of metformin in HS. METHODS: To assess the effect of metformin in vivo, we compared the immune and metabolic profiles of peripheral blood mononuclear cells (PBMCs) of patients with HS taking metformin vs. those not taking metformin. To examine the effect of metformin treatment ex vivo, we employed a skin explant model on skin biopsies from patients with HS not taking metformin, which we cultured with metformin overnight. We used enzyme-linked immunosorbent assays, multiplex cytokine assays and quantitative real-time polymerase chain reaction (RT-PCR) to measure inflammatory markers, and Seahorse flux technology and quantitative RT-PCR to assess glucose metabolism. RESULTS: We showed that metabolic pathways are dysregulated in the PBMCs of patients with HS vs. healthy individuals. In metformin-treated patients, these metabolic pathways were restored and their PBMCs had reduced inflammatory markers following long-term metformin treatment. In the skin explant model, we found that overnight culture with metformin reduced inflammatory cytokines and chemokines and glycolytic genes in lesions and tracts of patients with HS. Using in vitro assays, we found that metformin may induce these changes via the NLR family pyrin domain containing 3 (NLRP3) inflammasome and the AMP-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR) pathway, which is linked to glycolysis and protein synthesis. CONCLUSIONS: Our study provides insight into the mechanisms of action of metformin in HS. The anti-inflammatory effects of metformin support its use as a therapeutic agent in HS, while its effects on immunometabolism suggest that targeting metabolism is a promising therapeutic option in inflammatory diseases, including HS.

Targeting the NLRP3 inflammasome reduces inflammation in hidradenitis suppurativa skin.

BACKGROUND: Treatment for the debilitating disease hidradenitis suppurativa (HS) is inadequate in many patients. Despite an incidence of approximately 1%, HS is often under-recognized and underdiagnosed, and is associated with a high morbidity and poor quality of life. OBJECTIVES: To gain a better understanding of the pathogenesis of HS, in order to design new therapeutic strategies. METHODS: We employed single-cell RNA sequencing to analyse gene expression in immune cells isolated from involved HS skin vs. healthy skin. Flow cytometry was used to quantify the absolute numbers of the main immune populations. The secretion of inflammatory mediators from skin explant cultures was measured using multiplex and enzyme-linked immunosorbent assays. RESULTS: Single-cell RNA sequencing analysis identified a significant enrichment in the frequency of plasma cells, T helper (Th) 17 cells and dendritic cell subsets in HS skin, and the immune transcriptome was distinct and more heterogeneous than healthy skin. Flow cytometry revealed significantly increased numbers of T cells, B cells, neutrophils, dermal macrophages and dendritic cells in HS skin. Genes and pathways associated with Th17 cells, interleukin (IL)-17, IL-1ß and the NLRP3 inflammasome were enhanced in HS skin, particularly in samples with a high inflammatory load. Inflammasome constituent genes principally mapped to Langerhans cells and a subpopulation of dendritic cells. The secretome of HS skin explants contained significantly increased concentrations of inflammatory mediators, including IL-1ß and IL-17A, and culture with an NLRP3 inflammasome inhibitor significantly reduced the secretion of these, as well as other, key mediators of inflammation. CONCLUSIONS: These data provide a rationale for targeting the NLRP3 inflammasome in HS using small-molecule inhibitors that are currently being tested for other indications.

Innate lymphoid cell (ILC) subsets are enriched in the skin of patients with hidradenitis suppurativa.

Hidradenitis suppurativa (HS) is a chronic relapsing inflammatory skin disease manifested as painful inflamed lesions including deep-seated nodules, abscesses and sinus tracts. The exact aetiology of HS is unclear. Recent evidence suggests that immune dysregulation plays a crucial role in pathogenesis and disease progression. Innate lymphoid cells (ILC) are a recently identified immune cell subset involved in mediating immunity, however their role in HS has not yet been investigated. Three distinct subsets of ILC- ILC1, ILC2 and ILC3 have been described, and these are involved in skin tissue homeostasis and pathologic inflammation associated with autoimmunity and allergic diseases. In this study, we analysed by multiparameter flow cytometry the frequencies of ILC subsets in skin and peripheral blood mononuclear cells (PBMC) of HS patients and compared these to healthy control subjects and psoriasis patients. The absolute numbers of total ILC and subsets thereof were significantly reduced in the blood of HS patients relative to healthy controls. However, when patients were stratified according to treatment, this reduction was no longer observed in patients undergoing anti-TNF treatment. In HS lesional skin the absolute numbers of ILC were significantly increased relative to control skin. Furthermore, the frequencies of total ILC as well as ILC2 and ILC3 were significantly higher in non-lesional than lesional HS skin. This study analysed for the first time the presence of ILC subsets in the blood and skin of HS patients. Our findings suggest that ILC may participate in HS pathogenesis.

The mammalian target of rapamycin contributes to synovial fibroblast pathogenicity in rheumatoid arthritis.

Objectives: The mammalian target of Rapamycin (mTOR) is a metabolic master regulator of both innate and adaptive immunity; however, its exact role in stromal cell biology is unknown. In this study we explored the role of the mTOR pathway on Rheumatoid Arthritis synovial fibroblast (RASF) metabolism and activation and determined if crosstalk with the Hippo-YAP pathway mediates their effects. Methods: Primary RA synovial fibroblasts (RASF) were cultured with TNFα alone or in combination with the mTOR inhibitor Rapamycin or YAP inhibitor Verteporfin. Chemokine production, matrix metalloproteinase (MMP) production, and adhesion marker expression were quantified by real-time PCR, ELISA, and/or Flow Cytometry. Invasion assays were performed using Transwell invasion chambers, while wound repair assays were used to assess RASF migration. Cellular bioenergetics was assessed using the Seahorse XFe96 Analyzer. Key metabolic genes (GLUT-1, HK2, G6PD) were measured using real-time PCR. Reanalysis of RNA-Seq analysis was performed on RA (n = 151) and healthy control (HC) (n = 28) synovial tissue biopsies to detect differential gene and pathway expression. The expression of YAP was measured by Western Blot. Results: Transcriptomic analysis of healthy donor and RA synovial tissue revealed dysregulated expression of several key components of the mTOR pathway in RA. Moreover, the expression of phospho-ribosomal protein S6 (pS6), the major downstream target of mTOR is specifically increased in RA synovial fibroblasts compared to healthy tissue. In the presence of TNFα, RASF display heightened phosphorylation of S6 and are responsive to mTOR inhibition via Rapamycin. Rapamycin effectively alters RASF cellular bioenergetics by inhibiting glycolysis and the expression of rate limiting glycolytic enzymes. Furthermore, we demonstrate a key role for mTOR signaling in uniquely mediating RASF migratory and invasive mechanisms, which are significantly abrogated in the presence of Rapamycin. Finally, we report a significant upregulation in several genes involved in the Hippo-YAP pathway in RA synovial tissue, which are predicted to converge with the mTOR pathway. We demonstrate crosstalk between the mTOR and YAP pathways in mediating RASF invasive mechanism whereby Rapamycin significantly abrogates YAP expression and YAP inhibition significantly inhibits RASF invasiveness. Conclusion: mTOR drives pathogenic mechanisms in RASF an effect which is in part mediated via crosstalk with the Hippo-YAP pathway.

B-cell and complement signature in severe hidradenitis suppurativa that does not respond to adalimumab.

BACKGROUND: Hidradenitis suppurativa (HS) is a chronic inflammatory skin disorder with significant morbidity. The pathogenesis remains incompletely understood although immune dysregulation plays an important role. It is challenging to treat and approximately 50% of patients respond clinically to adalimumab, the only licensed treatment. OBJECTIVES: To examine differences between lesional and nonlesional HS skin at baseline using bulk RNA sequencing, and to compare the transcriptome in the skin before and after 12 weeks of treatment with adalimumab. To examine transcriptomic differences between adalimumab responders and nonresponders using Hidradenitis Suppurativa Clinical Response and the International Hidradenitis Suppurativa Severity Score System (IHS4); and to compare transcriptomic differences based on disease severity (Hurley stage and IHS4). METHODS: We completed bulk RNA sequencing on lesional and nonlesional skin samples of patients before and after 12 weeks of treatment with adalimumab. RESULTS: Baseline differentially expressed genes and pathways between lesional and nonlesional skin highlighted chemokines and antimicrobial peptides produced by keratinocytes; B-cell function; T-cell-receptor, interleukin-17 and nuclear factor-κB signalling; and T-helper-cell differentiation. Transcriptomic differences were identified in lesional skin at baseline, between subsequent responders and nonresponders. Patients with severe HS who did not respond to adalimumab had enriched complement and B-cell activation pathways at baseline. In addition, logistic regression identified CCL28 in baseline lesional HS skin as a potential biomarker of treatment response. CONCLUSIONS: This highlights the potential for targeting B-cell and complement pathways in HS treatment and the potential of stratifying patients at baseline to the most suitable treatment based on the skin transcriptome. CCL28 has not previously been identified in HS skin and has potential clinical relevance due to its antimicrobial function and homing of B and T cells at epithelial surfaces. Our results provide data to inform future translational and clinical studies on therapeutics in HS.

Proximal Humerus Fractures: Leave It Alone, Fix It, Replace It?

Proximal humerus fractures are common injuries that account for 10% of all fractures in the elderly. Several options are available for the management of proximal humerus fractures. Optimal treatment is based on the fracture pattern and the patient characteristics. Most of these fractures are minimally displaced and managed nonsurgically. Approximately 15% of proximal humerus fractures are comminuted, head-split, fracture-dislocation, or severely displaced, which make the best treatment option more challenging. Hemiarthroplasty is still a viable option in selected patients of these groups; however, advancements in locking plate designs and introduction of reverse total shoulder arthroplasty have led to better clinical outcome in meticulously selected patients. Nonetheless, the debate continues regarding the best management. It is important to discuss the best treatment options based on current literature.

Functional biomechanical comparison of Latarjet vs. distal tibial osteochondral allograft for anterior glenoid defect reconstruction.

INTRODUCTION: Glenoid reconstruction is indicated for recurrent glenohumeral instability with significant glenoid bone deficiency. Coracoid autograft (Latarjet) and distal tibial osteochondral allograft (DTA) reconstructions have been used to successfully restore glenohumeral stability. Relative advantages and disadvantages associated with each reconstruction technique have been described. However, direct comparisons of functional glenohumeral biomechanics associated with Latarjet vs. DTA reconstruction are lacking. This study was designed to compare these 2 glenoid reconstruction techniques with respect to joint kinematics and cartilage pressure mapping using a robotic testing system. METHODS: In accordance with institutional review board policies, human cadaveric shoulders (n = 8) were cyclically tested in the neutral position and 90° of external rotation with 60° and 90° of abduction under a 45-N joint-compression load to measure clinically relevant translations, loads, and torques. Joint contact pressure maps were obtained under a 120-N joint-compression load using pressure mapping sensors. After confirming that a 25% anterior glenoid defect resulted in glenohumeral dislocation, testing was performed to compare 3 conditions: native intact glenoid, 25% anterior glenoid defect with Latarjet reconstruction, and 25% anterior glenoid defect with DTA reconstruction. Analyses of variance and t tests were used to analyze data with statistical significance set at P < .05. RESULTS: Significant differences in anterior translation, inferior drawer, anterior drawer, compression loads, horizontal abduction, negative elevation (adduction), and external rotation torques during cyclical testing in 90° of external rotation with 60° and/or 90° of abduction were noted when comparing the 2 different glenoid bone reconstruction techniques to native, intact shoulders. The only significant difference between Latarjet and DTA reconstructions for measured translations, loads, and torques was a significantly higher absolute maximum compressive load for Latarjet compared to DTA at 60° of abduction. CONCLUSION: Latarjet coracoid osseous autograft and distal tibial osteochondral allograft reconstructions of large (25%) glenoid bone defects prevent failure (dislocation) and are associated with significant glenohumeral kinematic differences that largely confer less translation, load, and torque on the joint in abduction when compared to the native state. These findings suggest that these 2 surgical techniques exhibit similar glenohumeral kinematics such that each provides adequate functional stability following anterior glenoid bone reconstruction. Joint compression load and articular contact pressure distribution may favor distal tibial osteochondral allograft reconstruction for treatment of large (25%) anterior glenoid bone defects associated with shoulder instability.

Prevalence of cerebrovascular accidents in patients with ulcerative colitis in a single academic health system.

In general, IBD increases arteriovenous thromboembolic events, though the association between UC and cerebrovascular complications remains inconclusive. Some studies suggest young women with UC have an increased risk of cerebrovascular accidents (CVA). The focus of this study was to characterize the rates, anatomic distribution, and risk factors for CVA in patients with UC. We developed a retrospective cohort of patients with UC at a single health care system from June 2010 to June 2015. Neuroimaging was used to document presence, location and type of stroke and traditional risk factors were considered. Prevalence of CVAs in patients with UC was compared to that of the general population of Minnesota (MN) and the United States (U.S.). A total of 2,183 UC patients were identified (1088 females [f-UC], 1095 males [m-UC]). The prevalence of CVA in UC patients (4.7%, 95% CI 3.9-5.6) was higher than in the U.S. (2.5-2.7%, p < 0.0001) and in Minnesota (1.8% CI 1.5-2.2, p < 0.0001) . The prevalence increased in both sexes with a peak prevalence of 24.7% (95% CI 17.1-34.4) in women with UC over the age of 80. Older age, cancer and atrial fibrillation were risk factors for CVA in univariate analysis for both sexes. In multifactorial analysis, both age and atrial fibrillation were risk factors for CVA in the m-UC cohort, but only age was associated with CVA in f-UC. The most common type of CVA was ischemic stroke (77.7%). The most common locations for CVAs in UC patients were frontal and occipital lobes (19% and 18%, respectively). UC patients have an increased risk for CVA, with women over 80 demonstrating the highest risk. Providers should be aware of these risks in making treatment decisions for UC.

Extracranial arteriovenous malformations demonstrate dysregulated TGF-ß/BMP signaling and increased circulating TGF-ß1.

Extracranial arteriovenous malformations (AVMs) are characterized by anomalous arterial-to-venous connections, aberrant angiogenesis, local inflammation and hypoxia, and disorganized histological architecture; however, the precise molecular perturbations leading to this phenotype remain elusive. We hypothesized that extracranial AVM tissue would demonstrate deregulation of the TGF-ß/BMP signaling pathway, which may serve as a potential target in the development of molecular-based therapies for AVMs. AVM tissue was harvested during resection from 10 patients with AVMs and compared to control tissue. Blood was collected from 14 AVM patients and 10 patients without AVMs as controls. Expression of TGF-ß/BMP pathway components was analyzed using RT-PCR, western blotting, and immunohistochemistry. Circulating levels of TGF-ß1 were analyzed by ELISA. Paired t tests were utilized to perform statistical analysis. The mRNA levels of TGF-ß1, ALK1, Endoglin (ENG), Smad6, Smad7, and Smad8 were significantly elevated in AVM tissue when compared to controls. Protein levels of TGF-ß1 and Smad3 were elevated in AVM tissue while protein levels of BMP-9, ALK1, Smad1, Smad6, and Smad8 were significantly decreased in AVMs. Immunohistochemistry demonstrated increased TGF-ß1 in the perivascular cells of AVMs compared to normal controls, and circulating levels of TGF-ß1 were significantly higher in AVM patients. Patients with AVMs demonstrate aberrant TGF-ß/BMP expression in AVM tissue and blood compared to controls. Targeting aberrantly expressed components of the TGF-ß/BMP pathway in extracranial AVMs may be a viable approach in the development of novel molecular therapies, and monitoring circulating TGF-ß1 levels may be a useful indicator of treatment success.

Distinct stromal and immune cell interactions shape the pathogenesis of rheumatoid and psoriatic arthritis.

OBJECTIVES: Immune and stromal cell communication is central in the pathogenesis of rheumatoid arthritis (RA) and psoriatic arthritis (PsA), however, the nature of these interactions in the synovial pathology of the two pathotypes can differ. Identifying immune-stromal cell crosstalk at the site of inflammation in RA and PsA is challenging. This study creates the first global transcriptomic analysis of the RA and PsA inflamed joint and investigates immune-stromal cell interactions in the pathogenesis of synovial inflammation. METHODS: Single cell transcriptomic profiling of 178 000 synovial tissue cells from five patients with PsA and four patients with RA, importantly, without prior sorting of immune and stromal cells. This approach enabled the transcriptomic analysis of the intact synovial tissue and identification of immune and stromal cell interactions. State of the art data integration and annotation techniques identified and characterised 18 stromal and 14 immune cell clusters. RESULTS: Global transcriptomic analysis of synovial cell subsets identifies actively proliferating synovial T cells and indicates that due to differential λ and κ immunoglobulin light chain usage, synovial plasma cells are potentially not derived from the local memory B cell pool. Importantly, we report distinct fibroblast and endothelial cell transcriptomes indicating abundant subpopulations in RA and PsA characterised by differential transcription factor usage. Using receptor-ligand interactions and downstream target characterisation, we identify RA-specific synovial T cell-derived transforming growth factor (TGF)-ß and macrophage interleukin (IL)-1ß synergy in driving the transcriptional profile of FAPα+THY1+ invasive synovial fibroblasts, expanded in RA compared with PsA. In vitro characterisation of patient with RA synovial fibroblasts showed metabolic switch to glycolysis, increased adhesion intercellular adhesion molecules 1 expression and IL-6 secretion in response to combined TGF-ß and IL-1ß treatment. Disrupting specific immune and stromal cell interactions offers novel opportunities for targeted therapeutic intervention in RA and PsA.

The role of mitochondria in anchoring dynein to the cell cortex extends beyond clustering the anchor protein.

Organelle distribution is regulated over the course of the cell cycle to ensure that each of the cells produced at the completion of division inherits a full complement of organelles. In yeast, the protein Num1 functions in the positioning and inheritance of two essential organelles, mitochondria and the nucleus. Specifically, Num1 anchors mitochondria as well as dynein to the cell cortex, and this anchoring activity is required for proper mitochondrial distribution and dynein-mediated nuclear inheritance. The assembly of Num1 into clusters at the plasma membrane is critical for both of its anchoring functions. We have previously shown that mitochondria drive the assembly of Num1 clusters and that these mitochondria-assembled Num1 clusters serve as cortical attachment sites for dynein. Here we further examine the role for mitochondria in dynein anchoring. Using a GFP-αGFP nanobody targeting system, we synthetically clustered Num1 on eisosomes to bypass the requirement for mitochondria in Num1 cluster formation. Utilizing this system, we found that mitochondria positively impact the ability of synthetically clustered Num1 to anchor dynein and support dynein function even when mitochondria are no longer required for cluster formation. Thus, the role of mitochondria in regulating dynein function extends beyond simply concentrating Num1; mitochondria likely promote an arrangement of Num1 within a cluster that is competent for dynein anchoring. This functional dependency between mitochondrial and nuclear positioning pathways likely serves as a mechanism to order and integrate major cellular organization systems over the course of the cell cycle.

The impact of stress on social behavior in adult zebrafish (Danio rerio).

Stress has adverse effects on social behavior that is mediated by dopamine circuits in the midbrain. The purpose of this research is to examine the effect of chronic stress and dopamine signals on social behavior in zebrafish (Danio rerio). Chronic stress was induced chemically with low dosage of ethanol (0.25% for 5 days), and psychosocially with isolation (3-5 days) or overcrowding (5 days). Dopamine activity was decreased by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) exposure. Social behavior was observed by introducing one treated zebrafish to a group of four control zebrafish and measuring the nearest neighbor distance (NND). Swimming ability was analyzed by measuring total swim distance and average velocity. Analysis of swim ability showed that treatment had no adverse effect upon locomotor functioning. However, stress and MPTP affected social behavior similarly. In all stress conditions, there was a significant increase in NND (7.4±3.9-9.1±4.4 cm). MPTP also caused an increase in NND (8.9±2.7 cm), but MPTP/isolation treatment did not amplify the effect (8.9±5.5 cm). One possible explanation is that chronic stress causes a change in dopamine activity and decreases social behavior, providing insight into the function of dopamine in social behavior.

Rexinoids as Therapeutics for Alzheimer's Disease: Role of APOE.

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by amyloid plaques, composed of amyloid-beta peptide (Aß) and neurofibrillary tangles, composed of aberrantly phosphorylated tau. APOE4 is the greatest genetic risk factor for AD, increasing risk up to 12- fold with a double allele compared to APOE3. In contrast, APOE2 reduces AD risk ~2-fold per allele. Accumulating evidence demonstrates that apolipoprotein E4 (apoE4) plays a multifactorial role in AD pathogenesis, although the exact mechanisms remain unclear. Further data support roles for apoE4 as a toxic gain of function or loss of positive function in AD, a discrepancy that has significant implications for the future of apoE-directed therapeutics. However, recent evidence repurposing retinoid X receptor (RXR) agonists, or rexinoids, for the treatment of AD demonstrates conflicting, though potentially beneficial effects in familial AD-transgenic (FAD-Tg) mouse models. Of particular note is bexarotene (Targretin®), a selective rexinoid previously utilized in cancer treatment emerging as a viable candidate for AD clinical trials. However, the mechanism of action of bexarotene and similar rexinoids remains controversial, particularly in the context of human APOE. In addition, rexinoids demonstrate distinct adverse event profiles in humans that may have greater detrimental effects in an elderly AD population. Therefore, this special issue review discusses the implications for rexinoiddirected therapeutic strategies in AD, the potential mechanistic targets, and future directions for the improvement of rexinoid-based therapies in AD.

The APOE4 allele shows opposite sex bias in microbleeds and Alzheimer's disease of humans and mice.

The apolipoprotein APOE4 allele confers greater risk of Alzheimer's disease (AD) for women than men, in conjunction with greater clinical deficits per unit of AD neuropathology (plaques, tangles). Cerebral microbleeds, which contribute to cognitive dysfunctions during AD, also show APOE4 excess, but sex-APOE allele interactions are not described. We report that elderly men diagnosed for mild cognitive impairment and AD showed a higher risk of cerebral cortex microbleeds with APOE4 allele dose effect in 2 clinical cohorts (ADNI and KIDS). Sex-APOE interactions were further analyzed in EFAD mice carrying human APOE alleles and familial AD genes (5XFAD (+/-) /human APOE(+/+)). At 7 months, E4FAD mice had cerebral cortex microbleeds with female excess, in contrast to humans. Cerebral amyloid angiopathy, plaques, and soluble Aß also showed female excess. Both the cerebral microbleeds and cerebral amyloid angiopathy increased in proportion to individual Aß load. In humans, the opposite sex bias of APOE4 allele for microbleeds versus the plaques and tangles is the first example of organ-specific, sex-linked APOE allele effects, and further shows AD as a uniquely human condition.

Genetics ignite focus on microglial inflammation in Alzheimer's disease.

In the past five years, a series of large-scale genetic studies have revealed novel risk factors for Alzheimer's disease (AD). Analyses of these risk factors have focused attention upon the role of immune processes in AD, specifically microglial function. In this review, we discuss interpretation of genetic studies.  We then focus upon six genes implicated by AD genetics that impact microglial function: TREM2, CD33, CR1, ABCA7, SHIP1, and APOE. We review the literature regarding the biological functions of these six proteins and their putative role in AD pathogenesis. We then present a model for how these factors may interact to modulate microglial function in AD.